Tube-bending mandrel



-1 41. R. TTRADGE. Er AL 425, 9

TUBE-SENDING MANDREL.

Filed May a} 1945 cub-.-

l E 2 E a E L FIG.

'INVENTORS RICHARD F. ATTRIDGE ERNEST J- BLOUIN av M I ATTORNEY Patented Aug. 12, 1947' UNITED s'r' res PATENT OFFICE TUBE-BENDING MANDREL Richard F. Attridge, Revere, and Ernest J.

, Blouin, Salem, Mass.

2 Claims.

amended April 30, 1928; 370 O. G. 757) Our invention relates to a tube-bending man drel. It has to do more particularly, with a mandrel adapted to be disposed within a tube and having a flexibly mounted bearing unit located where the'tube is to be bent in order to maintain the cross-sectional shape of the tube during bending.

In bending thin-wall metal tubes at present, especially with short-radiusbends, it is customary to pack the tube with sand or fill, it with molten resin which is allowed to solidify in order to prevent collapse of the tube at the bend. The tendency for the outer side of the tube to collapse is caused by the extreme tension developed in the material 01 the outer side during the bending operation. The sand or resin used in an attempt to prevent collapse of the tube is emoved after bending the tube. Obviously, this method is slow and cumbersome.

A mandrel has been designed and used in an attempt tomaintain the cross-sectional shape of the tube at the bend. This mandrel includes a rod having a ball swiveled on its end. The ball is adapted to be disposed within the tube where it is bent to prevent collapse thereof. We have found that the bali'does'not keep the tube from flattening on the outer side of the bend. especially when the tube is being bent to a short radius This is due to the fact that the ball does not afford a bearing surface of sufilcient extent lengthwise of the bend. Consequently, the flattening of the tube on the outer side of the bend usually occurs beyond the ball. Also, the ball is not mounted in a sufflciently flexiblev manner to permit it to swing properly with the tube as it is being bent.

One of the objects of our invention is to provide a tube-bending mandrel having means associated therewith for effectively maintaining the crosssectional shape of the tube at the bend.

Another object of our invention is to provide a mandrel of the type indicated having a bearing unit of such a nature that it will afford sumcient bearing surface to prevent flattening of the tube on the outer side of the bend.

Another object of our invention is to provide a mandrel of the type indicated having the bearing unit mounted in a sumciently flexible manner to on: ennrnrl nnm't'. in? means: M n .elnnve rliem ml therebetween. All of these parts are carried by a cable which is connected to the end of the rod. The preferred embodiment of our invention is illustratedin the accompanying drawing wherein similar characters of reference designate corresponding parts and wherein: I

Fig. 1 is a plan view, partly broken away, illustrating our tube-bending mandrel in position in the line 44 of Fig. 2.

With reference to the drawing, we have illustrated' in Fig. l, clamping units I and 2 of a tubebending machine. These units l and 2 are of the usual type, the unit I being mounted in a fixed position and the unit 2 being mounted for swing-- ing'movement about a pivot point 3. This pivot point 3 is the center about which the tube 4 is to be bent. Initially, the clamping. unit 2 is disposed directly adjacent to the unit I, as indicated by the dotted lines, so that these units are in sideby-side relationship. When the tube 4 is being bent,-the unit Z'is swung about the pivot 3 and may, if desired, be swung through an angle of to the full-line position indicated in Fig. l. The unitl and the unit' 2 are provided with the usual tube-embracing dies which are opened and closed by handwheels 5 and 6, respectively.

A mandrel is inserted in the tube 4 before it is bent. The mandrel is secured in a fixed position within tube 4, prior to' bending the tube, by suitable means (not shown) attached to the bending machine. The mandrel I includes a rod having its inner end 8 threaded for receiving the threaded end of a sleeve 9. This sleeve 9 is of the same diameter as the internal diameter of the tube 4 to be bent. The sleeve 9 includes a bore Ill through which a flexible metal cable I! passes. The cable is attached to the sleeve by means of a bushing I! which fits into a complemental socket no at the inner end of bore Ill. The inner 'end of the cable II is secured to bushing l2 by the use of a wedge member I3 which expands the cable into a flared socket It in bushin 12, and by the use of solder indicated by numeral ii. The outer end of bore i0 is flared to form a chamber I6 which facilitates swinging of the cable l I in all directions relative to the sleeve.

The cable H extends a considerable distance from the end of the sleeve 9. This extending portinn nf the nahln mar-vine this lnnarinn unit [1 nf 3 our invention. This bearing unit consists of balls l8 and I8, and a ball spacer 20. all of which are preferably formed of case-hardened steel.

Each of the balls I 8 and I9 is of a diameter corresponding to the internal diameter of the tube 4 to be bent. Each of the balls has a bore II, of cross-sectional area somewhat larger than.

that of the cable, extending thereth'rough and through which the cable ll passes. Each of the bores Zl'has flaring ends 22 to facilitate swinging of the cable ll relative to'the balls in all directions. The extreme outer end of the cable is secured in one of the flared sockets 22 of ball I! by a wedge member 23 and solder, similar to the manner in which the opposite end of the cable is secured to the member l2. The spaced sleeve 20 has an internal diameter considerably larger than the cable ii so that it will be loose thereon and has an external diameter considerably less than that of the balls. The ends of the spacer sleeve 20 are flared to provide a bearing socket in each end for the adjacent ball. The extreme edges of the sleeve 20 are machined to form curved seats 20a for the balls.

In bending the tube, the unit 2 is positioned in the dotted-line position indicated in Fig. 1 and the mandrel I is anchored in position on the machine. The mandrel will carry one of our bearing units I! which will have balls of a diameter equal to the internal diameter of the tube to be bent and a sleeve 9 of corresponding diameter. The tube will be in the straight line position indicated by the dotted lines in Fig. 1. The mandrel will b so positioned that the outer end of sleeve 9 will lie in substantially the same plane as the center of pivot 3.

The machine is now operated to swing the unit 2 around the pivot 3. In the example shown, the unit 2 is swung through 180 but it is to be understood that it may be swung through any selected angle. to bend the tube to any desired extent.

The bending of the tube may be considered as occurring in successive increments of length about a point at the center of the end of sleeve 9. Resistance to bending sets up tension on the outer side of the bend of the tube which tends to cause the tube to collapse or flatten. However, the outer side of the bend of the tube is supported against the spherical surfaces of balls 18 and I! which are spaced sumciently to hold the tube in its circular form. The bearing surface of the outermost ball l9 will be located a cohsiderable distance from the end of sleeve 9. This is accomplished by employing two balls and the spacer 20 and by having cable ll of a suillcient length to permit the inner ball iii to move a considerable distance from the outer end of sleeve 9. As the tube bends, the bearing unit I! will readily flex and move with it, due to the flexible cable I l and also due to the fact that both the balls l8 and I! will rock in the bearings in the ends of the sleeve 20. The surfaces of the balls engage the throat or inner side of the bend of the tube and will keep it in contact with the curved portion 24 of the. die unit 2. Such I portion 24 will be of a radius of curvature corresponding to that to be produced on the throat or inner side of the bend. Thus,ilattening of the 5 outer side of the bend is prevented while the inner side is caused to effectively contact with the curved part 24 of the die.

After the tube is bent as indicated, the handwheels 5 and 6 are actuated to operate the dies to release the tube. Then it is merely necessary to grasp the curved portion of the tube and pull the tube out of the dies and off the mandrel.

It will b apparent from the above description that we have provided a bearing unit on a tubebending mandrel having a number of advantages.

The bearing unit will provide suflicient bearing surface, properly located, to prevent flattening of the outer side of the bend of the tube. The bear.- ing unit is mounted'flexibly and is flexible in itself and, consequently, will properly position and adjust itself during the bending of the tube.

Various other advantages will be apparent.

The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalty thereon or therefor.

Having thus described our invention, what we claim is:

1. In a tube-bending mandrel, a sleeve of substantially the same diameter as the tube to be bent attached to the end of the mandrel, a flexible cable anchored within said sleeve and extending through a flared opening in the outer end thereof, a plurality of separate balls carried by the extending end of said cable and having a diameter corresponding to that of the internal diameter of the tube, a spacer sleeve carried by the cable between the balls and having flared sockets in its ends in which said balls rock, the outer end of said cable being anchored to the outermost ball.

2. A tubebending mandrel comprising, a bearing unit adapted to be positioned within the tube 45 where it is to be bent, said bearing unit including a pair of separate ball members which correspond in diameter to the internal diameter of the tube, said ball members being spaced apart by a spacer sleeve, said spacer sleeve having bear- 50 ing sockets in each end and in which the adjacent ball members rock, and a flexible member carrying said ball members and said spacer sleeve.

RICHARD F. ATTRIDGE. ERNEST'J. BLOUIN.

REFERENCES CITED The following references are of record in the flle of this patent:

1,856,597 Stjarnstrom May 3,1932 

